It is previously known, e.g. at a front door, to attach an optical observation port assembly extending through the door, in order to obtain visual control of persons outside the door, before the door is opened; said previously known type of observation port includes an optical lense system, thus permitting a certain panoramic or wide angle effect.
However, it is a well known fact that this previously known type of observation port does not permit viewing of people or objects within such a large viewing sector, that the area outside the door can be completely viewed. Persons, or objects, have therefore been concealed from the eye of the viewer. As a consequence, concealed weapons and other objects have been surprisingly used against the viewer, when the door has been opened.